What does a double question mark do in C#? [duplicate]

Possible Duplicates:
?? Null Coalescing Operator --> What does coalescing mean?
What do two question marks together mean in C#?

I couldn't find this question being asked here so I figured I would ask it. What does a double question mark do in C#?

Example:

x = y ?? z;

Solution 1:

This is a null coalescing operator. The method above states x is assigned y's value, unless y is null, in which case it is assigned z's value.

Solution 2:

From Wikipedia:

It's the null-coalesce operator and shorthand for this:

x = (y != null ? y : z);

Solution 3:

Use y if not null, otherwise use z.

Solution 4:

If a the value y is null then the value z is assigned.

For example:

x = Person.Name ?? "No Name";

If name is null x will have the value "No Name"